Various methods for manufacturing ballistic helmets are widely known. Following WWII, metal military helmets began to be largely replaced by helmets made of plastics combined with various other materials. Some helmets began utilizing aramid fiber materials for their ballistic and lightweight properties, for example. Woven aramid fiber materials were often pattern cut and molded into helmets. Composite helmets were made using pieces of fabric impregnated with resin or other ballistic sheet material where the fabric was cut into shapes and then arranged in a mold subjected to heat and pressure. In general, these types of processes were time consuming and resulted in significant quantities of costly scrap material.
One past method of making ballistic helmets included making a laminated ballistic helmet from plural, continuous filament resin-coated layers, as set forth in U.S. Pat. No. 4,199,388 to Tracy et al. This type of operation produced multiple helmet-shaped preforms which could be stacked together and molded in a heated metal compression mold.
In other specific examples, composite helmets were formed from impregnated fabric cut into a pinwheel shape where crowns of the pinwheel were placed on top of one another such that their petals were in staggered relationship. The preform was placed in a heated mold subjected to compression and heat to form a helmet. Other methods attempted to improve this technique by more efficient cutting of the fabric, such as along a zig-zag line according to the method discussed in U.S. Pat. No. 4,656,674 to Medwell. Similarly, U.S. Pat. No. 4,778,638 to White taught making a helmet by layering hexagonal blanks in a mold to form plies.
U.S. Pat. No. 7,228,571 to Cheese taught a technique of making a helmet from a sheet of resin-impregnated fabric. This included cutting curved blanks from a sheet, stacking the sheets into a preform, and molding the helmet from the preform.
Recent methods have been described in which flat patterns were cut from the materials chosen for helmet construction. These materials were forced into a steel mold having the outer shape of the helmet by using a punch that defined the interior shape of the helmet. Thermoplastic advanced composites were used in these processes, where reinforcing fibers were embedded in a matrix of thermoplastic resin to offer high specific strength and stiffness and low density. Further, including an inner aramid composite anti-ballistic liner and an outer carbon-fiber-reinforced thermoplastic shell has been suggested as well.
Despite the advances in making protective helmets, most of these processes continue to result in significant quantities of costly wasted material. Manufacturing according to these methods remains time-intensive and labor-intensive in most cases and significant room for improvement exists in helmet design and performance. In addition to the considerable time and labor that was generally involved in attempting such techniques, properly forming the helmet was a challenge. For example, wrinkling of the ballistic material in recent thermoplastic advanced composite methods has been a problem as well as ensuring that helmets have a uniform or desired thickness.
Accordingly, advances in the area of military helmet technology continue to be desired as such equipment can be vital to the safety of persons, including armed forces located around the world. Moreover, improved helmets, including those with enhanced ballistic performance, greater ease of manufacture, reduced weight and more uniform and effective structural properties are widely sought.